This invention relates to concrete roof structural systems which are post-tensioned or pre-stressed and which are erected into a dual or multiple sloped shape using either precast panels or a monolithic poured-in-place concrete slab. In almost all cases, it consists of wood trusses assembled with 2".times.4" or 2".times.6" (nominal dimensions) structural grade wood sections and covered with no less than 5/8" plywood sheathing. Many years ago, before the wood truss came into being, this system consisted of wood rafters covered with wood boards. At present most of these roofs remain in place, but all of them are still exposed to the fury of hurricanes, the threat of fires and the hunger of termites, let alone the devastating effect of tornadoes. In addition, the waterproofing qualities of these roofs are affected after a relative few years (in many cases less than 15) and the roofing has to be replaced at the corresponding cost.
Some thirty five years ago the marketplace mentality for multi-story buildings, gymnasiums, warehouses and big span structures in general was geared around the structural steel frame, the open web steel joist, the steel deck, the gypsum board and the poured in place gypsum roof. Around 1965 the reinforced concrete structure became economically feasible, and as the contracting sector learned about the new system it rapidly penetrated the market. Today almost all these types of structures are geared around the many forms and systems of the reinforced concrete.
However, for almost all dwellings the wood truss as the roof structure has remained intact. No sensible changes have taken place in this sector of the building market. With Hurricane Andrew thousands of dwellings literally lost their roofs, and the Building Code had to be revised with the only system at hand, the wood truss and plywood sheathing.
Secular inflation has affected the building industry all along. As wood demand increased, its price and final cost increased. Year after year its price in the marketplace has increased from a very affordable one to a relatively expensive one. Parallel to it, the wood structural system cost for dwellings has also increased, and cost is expected to continue.
Quality comparison of the two systems, wood and concrete, gives the reinforced concrete structure concept the hands down advantage over the wood structural systems.
Structurally, the systems disclosed herein fully comply with the South Florida Building Code. The attached drawings represent a typical dwelling plan and sections describing some of the different structural details that occur at the roof level.